A friend had what I think was a Telstar Marksman in the late 70s. It was a console that had the usual Pong-like games built-in, and also came with a light gun for a target shooting game. It didn't take long to figure out you could "shoot" the ball in all the games, even the supposedly non-shooting ones. It was a fun way to annoy your friends.
I always wondered why a box flashes around the ducks whenever I took a shot. Now I know.
Although I certainly perceived it every time, not just when there were multiple targets (which is what the article claims). I don't recall perceiving the black frame, though.
This is related to the TV refresh rates. The system was designed for TVs that refreshed 30 times per second, the standard in japan. However the standard in either USA or Europe (I don't remember which) was 24 refreshes per second. This led to the flash of the screen being visible in some TVs
Now its simpler I believe. The screen is scanned by an electron beam, the gun senses the bright pulse when the beam passes the point its focused on, the game correlates pulse to screen position.
This is how the GunCon (Time Crisis) gun worked -- comparing the observed beam refresh with a feed of the video signal.
Unfortunately, this method requires a CRT, so these guns don't work with LCD or plasma displays. That's why modern light guns, like the GunCon 3, use a Wii-like system that triangulates position based on infrared LEDs attached to the display.
